Variable-resistance device



Janr 1, 1929. y 1,697,238

` N. c. GREENE VARIABLE RESISTANCE DEVICE Filed June 9, 1925 2 Sheets-Sheet 1 a E INVENTo JEM E4 da ATTORNEYS Jan. l, 1929. 1,697,238 A N. c. GREENE VARIABLE RESISTANCE DEVICE Filed June 9, 1925 2 Sheets-ShedI 2 T--lg 171g. s

:NVE ToR WMC Patented Jan.'1, 1929.

- UNITED sTAT'EsPATENr OFFICE.

'NATHANIEL C. GREENE, 0F NEW YORK, N. Y., ASSIGNOR TO POLYMET MANUFACTUR- ING CORPORATION, A CORPORATION OF NEW YORK.

VARIABLE-RESISTANCE DEVICE.

Application led June 9,

This invention relates generally to variable-resistance devices and more particularly to the type known as rheostats, as employed in the radio art or other similar electrical apparatus, wherein a variation of the strength of current flowing through the filaments of thermionic devices, such as audions, is an important. factor.

One of the objects of my invention is to provide a simple and efficient construction for a rheostat whereby the device can be quickly and operatively mounted as desired upon a panel, as in a radio receiving set.,` or on a board for other electrical work, either temporary or experimental, and which does not have to. be disassembled when changing from one type of mounting to another.

Another object of my invention is to provide a rheostat that can be easily and quickly disassembled should the user desire to do so, and which can be readily assembled without changing its original adjustment.

Another object of my invention is the construction of a rheostat having improved means to securely and firmly hold the resistance wire in posit-ion.

Another object of the invention is to provide a device of the character described which will be compact, simple in construction, economical to manufacture, efficient in operation, attractive in appearance and inexpensive to manufacture.

Another object of my invention is to provide a rheostat that canbe readily used as a potentiometer or as a combination rheostat and potentiometer without removing any of the parts when making the change.

With these and other objects in view, to be more fully set forth hereinafter, the invention consists in the novel construction7 combination of elements, and arrangement of parts, which will be exemplified in the operation and construction herein described in the following specification and illustrated in the accompanying drawings. y

The invention will first be described in connection with the accompanying drawings, wherein similar reference characters are used to designate corresponding parte throughout the several views, and more specifically defined and indicated in the appended claims.

Other objects and advantages of my invention will be in part evident y and in part pointed out more particularly hereinafter in connection with the description of an em- 1925. Serial No. 35,880.

vbodiment of my invention and the modified Fig. 1 is an elevational view of one formof my rheostat with the panel and dial in section;

Fig. 2 is an elevation of a fragment of a panel illustrating the single hole method of mounting my rheostat;

Fig. 3 is a rear view of my improved rheostat showing the essential parts;

Fig. 4 is a sectional view taken on the line 4-4 of Fig. 3;

Fig. 5 is a detail View of the spindle;

Fig. 6 is another detail view of the spinle lo5oking in the direction of the arrows in Fig. 7 is a detail plan view of the contact arm;

Fig. 8 is an enlarged longitudinal sectional view of a portion of the resistance coil and its insulator strip, illust-rating my improved mounting for the resistance coil;

Fig. 9 is a sectional view of my rheostat in a modified form;

Fig. 10 is a front elevation of a fragment of a panel illustrating the three hold method of mounting my modified fom;

Fig. 11 is a detail view of the spindle used in my modified form;

Fig. 12 is another detail View of the spindle looking in the direction of the arrows in Fig. 11;

Fig. 13 is a partial rear view ofmy improved rheostat illustrating it as a combination rheostat and potentiometer; and

Fig. 14 is a partial sectional view of the potentiometer terminal taken on the lin'e 14-14 of Fig. 13.

Referring to the drawings, 1 represents the usual panel of'board upon which the rheostat is mounted. The circular base 2 of molded insulating material has integral therewith the circular shoulder 3 around the outer surface of which is placed a resistance member 4 consistin of a fiat strip of insulating material 5 an a wire coil 6 made preferably of non-corrosive nichrome wire of practically a zero temperature coeficient, which I found to be superior for this specific use. The resistance wire when wound on the fiat strip of insulating material 4 is made to conform with the cross-section thereof as illustrated in Figures 4 and 9, and each turn of `said resistance wire is placed in a groove 7 cut in both edges of said insulating material 4 which is more clearly illustrated in Fig. 8, by so mounting the resistance Wire 6 the same is firmly and securely held in position and prevents the wire from moving and causing short circuits. The grooves 7 are cut to a depth equal to apportionately oneand 9, and the screws 10 and 10'r1 which hold said terminals securely in the counter-sunk portions 11 and 11a in base 2. The U shaped terminals are so constructed so as to provide the lugs 12 and 12a to which the lead wires may be soldered when in use. Oneend of the resistance coil is held in contact with the U shaped terminal 9 and the other end is fas'- tened into the flat strip of insulating material 5v a short distance away from the terminal 9a, so that the contact arm 19 can slide off the resistance coil to break the circuit. The U shaped terminals 9 and 9a project beyond the edge of the resistance member 4 to such an extent that they serve as stops for limiting the range of movement of the contact arm 19. i

The base 2 is provided with the central portion 13a and the hub 13 which is drilled and tapped .to receive the metal screw threaded bushing 14, the length of which is such as to provide for its extending beyond the base 2, as illustrated most clearly in Fig. 4. Upon the extended portion of the screw threaded bushing 14 is screwed the shouldered lock-nut 15, the purpose of which is more fully described herein. The screw threaded bushing 14 (see Fig. 4) reamed for the reception of the reduced portion of the spindle 16 which extends beyond the hub 13 of -the base 2, and through a hole for the purpose in one end of the bus-bar 17 which is securely held in position and in contact with the U shaped terminal 9 by the screw 10a. The check-nut 18 is turned up on the screw threaded end of the spindle 16 until it comes in close contact with, but not binding upon, the bus-bar 17. The contact arm 19, preferably made of phosphor bronze, is so constructed at one end to provide a contact point 20 to insure a smooth running contact`-with the resistance coil 6, and the other end has punched therein the hole 21, the sha-pe of which is such as to allow its being passed over the screw threaded end of the spindle 16 and the two flats 22 machinedthereon (see Figs. 5 and 6). The acorn nut 23 holds the contact arm 19 tightly up against the check nut 18, thus providmg perfect electrical contact with the operating parts. The

. countersunk hole 36 in the base 2 is used only when it is desired to have my rheostat act as is centrally drilled and a combination rheostat and potentiometer, whlch 1s more fully described hereinafter'.

By means of the set screw 24 the knob or' dial 25 is securely held in position upon the enlarged end of the spindle 16. lA rotary movement of the dial 25 either clockwise or counter-clockwise is immediately taken up by the contact arm 19 and this unison, although the contact arm 19 is not permanently fixed to the spindle 16, is solely obtained by means ofthe hole 21 and the flats 22 machined on the threaded end of the spindle. I

To mount my rheostat upon the panel 1, as shown in Fig. 1, a hole must first, be drilled therein which should be but a few thousandths larger than the diameter of the shoulderonthelock-nut 15. The next step is to take the dial 25 off the spindle 16 and then back off the lock-nut 15. The extended portion of the screw threaded bushing 14 is then inserted into the hole drilled into the panel and the lock-nut 15 screwed back into the position as illustrate-d, until the panel 1 is positively clamped between the under side of the base 2 and the hexagon head of the lock-nut. The dial 25 is then put back in position on the spindle 16 and the set screw 24 tightened up, making the rheostat ready for use. If a very thin panel is used for mounting, instead of a thick one as illustrated, the shoulder on the lock-nut 15 will enter the 'countersunk portion 132l of the base 2, insuring perfect clamping action without the aid of washers which is the common practice today.

Referring to the Figures 9, 10, 11. and 12, which illustrate a modified form of my invention, it will easily be seen that the resistance member and its supporting parts are identicalY with those already described herein, and that the only changes that have been made are in connection with the parts pertaining to the rotary movement of the contact arm, and the method of mounting my rheostat upon a panel, of which the following is a description.

The hub 13 of the base 2 (Fig. 9) has inwhich is ush with the under side of saidbase and the end of the hub. The bushing 26 is drilled and reamed for the reception of a reduced'portion 27 of the spindle 28 which is long enough to extend through and Hush with the outer face of the bus-bar' 17 as shown. The diameter of the screw threaded portion 29 of the spindle is smaller than that of the portion,27 and has the two Hats 30 machined thereon (Figs 11 and 12) the purpose of which has already been described herein. The acorn nut holds the contact arm 19 secure against the shoulder formed by the portion 27 and the. screw threaded portion 29.

The larve end of the spindle 28 passes through ahole in the panel 1, upon which is fastened the dial 31 by means of the set screw 32. This modified form of my invenlli tion is held in position upon the panel 1 by means of the screws 33 which pass through and into tapped holes (not shown) in the base 2.

In order to use my improved rheostat as a combination rheostat and potentiometer I have provided the countersunk hole 36 in the base 2. The bus-bar 17 is unfastened from the screw 10a (see Fig. 3) and moved in a clock-wise direction until the hole in the bus-bar registers with the countersunk hole 3G. (See Fig. 13.) A screw 36', long enough to pass through the base 2 and the bus-bar 17,`is then placed in position and the terminal post 35 is securely screwed down upon its projecting' end as illustrated in Fig. 14. The potentiometer lead wire is held in position by the round head screw 37.

While I have illustrated and described my invention, it Will be apparent. that it is by no means limited to the specific forms described, but that many modifications besides the one illustrated and described herein may be made without departing from the scope of my invention as set forth in the appended claims.

In accordance with the provisions of the patent statutes, I have described my invention together with the construction which I now consider to represent the best embodiment thereof, but I desire it understood that my invention is not confined to the particular form shown and described, the same being merely illustrative, and that the invention can be carried out in other ways Without departing from the spirit of my invention; and, therefore, I claim broadly the right to employ all equivalent instrumentalities coming within the scope of the appended claims, and by means of which objects of myl invention are attained, and new results accomplished, as herein s et forth, as it is obvious that the bus-bar pivoted upon said spindle in contact with said arm, means positioned at one of said lugs to engage the free end of said bus-bar, and a connecting terminal on said base between the extremities of said helix to also engage the free end of said bus-bar when the same is pivotally swung away from said lug, whereby said bus-bar may be swung on its pivot to electrically connect said helix through said contact arm alternatively with said lug or said terminal.

2. In a device of the character described, an insulating base, a resistance helix positioned on said base in the form of an arc, a spindle mounted in the base and in axial relation to said helix, a pair of spaced apart connecting terminals positioned upon said base at equal distances from said spindle, and apair of arms pivoted on said spindle, one of said arms contacting with said helix and the other of said armswhen swung on its pivot contacting with said terminals alternatively, whereby said arms may connect said helix alternatively with both of said terminal's.

This specification signed this 5th day of June, 1925.

NATHANIEL C. GREENE. 

